Scilab Function
Last update : 12/1/2004

portrait - 2 dimensional phase portrait.

### Calling Sequence

  `[]=portrait(f,[odem,xdim,npts,pinit])`

### Parameters

- `f`: a Scilab external which gives the field of the dynamical system. Hence it can be a macro name which computes the field at time t and point x [y]=f(t,x,[u]) or a list list(f1,u1) where f1 is a macro of type [y]=f1(t,x,u) or a character string. The macro can be used to simulate a continuous or discrete system and in case of discrete system the second parameter must be set to 'discrete'
- `options`: The other parameters are optional. If omitted they will be asked interactively
  - `odem`: gives the integration method to use. The value "default" can be used, otherwise see ode for a complete set of possibilities
  - `npts`: a vector of size (2,10) [number-of-points,step] gives the step for integration and the number of requested points. The solution will be calculated and drawn for time=0:step:(step*[number-of-points])
  - `xdim`: [xmin,xmax,ymin,ymax,zmin,zmax] the boundaries of the graphic frame.
  - `pinit`: initial values for integration. A set of initial points can be given in a matrix

              pinit = [x0(1), x1(1),...., xn(1)
                       x0(2), x1(2),...., xn(2)
                       x0(3), x1(3),...., xn(3)].

### Description

Interactive integration and display of a 2 dimensional phase portrait of a dynamical system dx/dt=f(t,x,[u]) (where u is an optional parameter )

### Examples

    a=rand(2,2)
    deff('[ydot]=l_s(t,y)','ydot=a*y')
    portrait(l_s)

### See Also

`ode`,